The invention relates to electrical energy management systems that shed and restore prioritized controlled loads in such a manner as to minimize peaking of power consumption of a residence with minimum impact on the life-style of residential occupants in order to maximize utility company revenue by keeping power consumption close to a level that utilizes as much as possible of the utility company's capacity to generate electrical power from hydroelectric, nuclear, coal-fired and other generating sources that have relatively low operating costs but require very large capital outlays to construct, thereby avoiding the need for the utility company to use oil or gas powered peak load generating sources that sharply increase the rates that must be charged to utility customers.
A number of power controllers or energy controllers useful for shedding and restoring controlled loads in a residence have been proposed, including those disclosed in commonly assigned copending applications "System and method for optimizing shed/restore operations for electrical laods", Ser. No. 191,424, filed Sept. 26, 1980 by Hedges et al. and "System and method for optimizing power shed/restore operations", Ser. No. 274,488 filed June 17, 1981 by Gurr et al. Commonly assigned issued U.S. Pat. No. 4,247,786 is deemed indicative of the state of the art. U.S. Pat. No. 3,652,838; U.S. Pat. No. 3,906,242; U.S. Pat. No. 4,023,043; U.S. Pat. No. 4,059,747; U.S. Pat. No. 4,064,485; U.S. Pat. No. 4,075,699; U.S. Pat. No. 4,146,923; U.S. Pat No. 4,168,491; U.S. Pat. No. 4,181,950; and U.S. Pat. No. 4,216,384 also are believed to be generally indicative of the state of the art for energy controllers.
The various energy controllers disclosed in these references are intended to keep peak power usage by residential customers approximately below a predetermined level while maintaining the total cumulative amount of energy used by customers relatively unchanged, thereby postponing use of certain electrical loads when such postponing does not cause undue inconvenience to the residential customers.
It has been found that energy controllers that make shed and restore decisions based on instantaneous power measurements sometimes cause an excessive number of switching operations turning controlled loads on and off under certain operating circumstances. For example, some energy controllers cause undesirable "cycling" to occur, wherein the system will automatically first shed a number of loads, then recognize within a short time that too many loads were shed, and then restore too many loads. This can result in faulty operation, reduced reliability and reduced useful life of many appliances and other electrical loads.
In some other instances, it has been found that certain high priority controlled loads are rarely switched off by prior controllers, and in other instances, low priority loads are switched off by the controller but are rarely switched back on.
Results of the present assignee's experimentation suggest that a fixed maximum peak load limit that, if exceeded, results in shedding of loads that can cause highly ineffective use of energy controllers during portions of the year when it is unlikely that high peak power consumption will occur even if no energy controller is used. For example, in a home heated by natural gas, excessive peaking of electrical power consumption normally will occur only in the summer. For example, assume that in such a home an energy controller begins shedding controlled loads at a predetermined demand limit of eight kilowatts in the summer when total power consumption with the air conditioning unit is turned on. It is quite likely that the energy controller will never shed any electrical load during the winter months because the five kilowatt air conditioner never turns on in the winter. Consequently, during the winter no benefit is obtained from the energy controller.
Nevertheless, relative peaking of the residence power consumption does occur, albeit at lower levels, in the winter for such a residence, and such relative peaking may occur within a price-sensitive power range. Any time substantial peaking of power consumption by a residence occurs within a price-sensitive power range, there is an opportunity for savings on the energy billing rate if some power usage during the peaking period can be postponed. Therefore, if prioritized load shedding and load restoring operations are performed, a reduced rate for that residential consumer can result, and this reduced rate can be achieved with minimum inconvenience to him if the energy controller is properly designed.
In most residences, there are a number of unpredictable temporary sharp increases in the amount of energy required by that residence. For example, overnight visits by a large number of guests may cause some energy controller programs to operate in a manner that is highly inconvenient to the residential customer.
There are certain situations, especially in commercial building having a large number of air conditioners, that present very difficult problems to any previously known peak power curtailment system. For example, imagine a long, narrow commercial building having its longitudinal axis directed east and west and having air conditioned offices in both the east and west portions of the building. In the morning hours, the offices on the east end of the building receive much more solar heat through their windows, and will need much more air cooling than is the case for offices on the west end of the building. No energy controller that allocates electrical power to the multiple air conditioners on the east and west ends of the building on an equal priority basis or a fixed priority basis is capable of providing substantially equal comfort to workers in both the east offices and west offices both during the morning hours and the afternoon hours. For example, not one of the sequential priority systems in the above-mentioned commonly assigned U.S. Pat. No. 4,211,933 by Hedges et al., the random priority scheme disclosed in U.S. Pat. No. 4,213,058 by Townsend, the rotating priority scheme (in which the first load to be shed is different each time a shed operation is carried out) disclosed in U.S. Pat. No. 4,064,485, or any of the systems disclosed in U.S. Pat. Nos. 2,714,453 by Delisle, 4,180,744 by Helwig, Jr., and 4,216, 384 by Hurley, can provide adequate load curtailment functions for the air conditioners of the above elongated commercial building without causing considerable discomfort to the occupants of the east and west offices on a hot day that severely taxes the capabilities of the air conditioning united used.
With use of any of the known prior schemes, it is possible to get into an "equilibrium condition". This situation can arise when the loads that are currently turned on actually maintain the average power consumption of the establishment or residence just below the predetermined threshold or power limit. This has the undesired effect of depriving controlled loads that are presently shed any opportunity to be restored at all.
None of the known references provides or suggests any "feedback" from the environment being controlled to the energy controller to affect future shed or restore decisions. Several of the prior art references do recognize the problem, but none provides any satisfactory solution--it is strictly "hit or miss" as to whether the known energy controllers accomplish the desired objectives in any particular environment.
It can be seen that despite all of the research and development that has occurred in the field of residential energy controllers in recent years, there still remains an unfulfilled need for a low cost, highly reliably automatic energy controller that substantially reduces peak power consumption by a residence without substantial inconvenience to certain users, thereby reducing energy billing rates for that user without unacceptable impact upon lifestyle or work environments and yet is flexible enough to allow temporary, relatively sharp transitory increases in power demand by the user without necessarily increasing the user's billing rate for an entire billing period.
Therefore, it is an object of the invention to provide an electrical energy controller for shedding and restoring loads to an establishment or residence to provide maximum use of energy up to a preselected demand limit with less impact on the user's comfort or life-style than is possible with known prior energy shedding and restoring devices and without subjecting the user to excessively high utility billing rates.
It is another object of the invention to provide an energy controller and method that will automatically seasonally adjust peak power consumption limits which, if exceeded by a residence or establishment, causes shedding of controlled loads.
It is another object of the invention to provide a power shed-restore system that avoids rapid "load cycling" that occurs under certain circumstances for certain known prior power shedding and restoring devices.
It is another object of the invention to provide an electrical energy shedding and restoring system that provides maximum energy utilization up approximately to a selected power limit with minimum impact on the lifestyle of an occupant of a residence or establishment, and with a minimum number of load switching operations.
It is another object of the invention to provide an electrical energy shedding and restoring system that dynamically allocates power to controlled loads at least partly on the basis of measurements of the effects that such controlled loads are intended to produce.
It is another object of the invention to provide an electrical energy shedding and restoring system that allows user selection of relative priority weights to be assigned to each controlled load and yet assumes that each load, regardless of its assigned weight, will have the opportunity to operate at least some of the time, at least partially on the basis of how long that controlled load has been shed.
It is another object of the invention to provide an electrical energy shedding and restoring system that avoids becoming stabilized in an undesired equilibrium condition.